Kinematic analysis of secondary faults within a distributed shear-zone reveals fault linkage and increased seismic hazard

Abstract

Complex multifault earthquake ruptures involving secondary faults emphasize the necessity to 21 characterize their seismogenic potential better and study their relationship with major faults to 22 improve the seismic hazard assessment of a region. High-resolution geophysical data were interpreted to make a detailed characterization of the Averroes Fault and the North Averroes Faults, which are poorly known secondary right-lateral strike-slip faults located in the central part of the Alboran Sea (western Mediterranean). These faults appear to have evolved since the Pliocene as part of a distributed dextral strike-slip shear zone in response to local strain engendered by the diverging movement of the Carboneras Fault to the north, and the Yusuf and Alboran Ridge faults to the south. In addition, the architecture of these faults suggests that the Averroes Fault may eventually link with the Yusuf fault, thus leading to a higher seismogenic potential. Therefore, these secondary faults represent a hitherto unrecognized seismogenic hazard since they could produce earthquakes up to moment magnitude (Mw) 7.6. Our results highlight the importance of the role played by secondary faults in a specific kinematic framework. Their reciprocal linkage and their mechanical relationship with the main faults could lead to future complex fault ruptures. This information could improve fault source and earthquake models used in seismic and tsunami hazard assessment in this and similar regions.

answer to the referee 2

“…The referee is right. The dataset in Perea et al, (2018) allows proposing a timing of propagation of secondary NW-SE dextral strike slip faults of the Yusuf fault system, which fits well with our results. These authors propose that early Pliocene subsidence occurred in the Djibouti plateau.…”

“…Estrada et al, 2018;Martínez-García et al, 2011). The northern segment of this structure is younger than 1.1Ma (Perea et al, 2018). On a regional scale, it draws a poorly continuous shear zone from the External Units in the Betic Belt to the Algerian Margin.…”

Slip Partitioning in the 2016 Alboran Sea Earthquake Sequence (Western Mediterranean)

“…The leftlateral Al-Idrisi fault is an important tectonic accident in the Alboran Sea, composed of a ∼60 km long, ∼N20°E striking northern segment, a ∼20 km long, N40°E striking central restraining bend and a southern segment striking ∼N10°E, with length of at least 20 km (Martínez García et al, 2011;Martínez García et al, 2013;Gràcia et al, 2019). At the northern termination, the Al-Idrisi fault ends at a network of secondary right-lateral faults that separate this fault from the offshore Carboneras fault (Perea et al, 2018). The southern segment reaches into an area of distributed transtensional deformation at the Moroccan margin (d 'Acremont et al, 2014; FIGURE 6 | (A) Fault model with 40 km length and 12 km width and slip initiation in the center (star), including two planar, N10°E and N40°E striking fault segments of the same length (perspective view from SE).…”

“…While the Alboran-Rif domain is characterized by conjugate strike-slip faulting with normal component, seismotectonics along the coast of Algeria and Tunisia is dominated by reverse faulting and right-lateral strike-slip, (e.g., Bezzeghoud and Buforn, 1999;Braunmiller and Bernardi, 2005;Stich et al, 2006;Soumaya et al, 2018). Over the recent decade, marine multibeam and seismic reflection imaging in the Alboran basin was able to characterize the principal active faults in the offshore part of the Alboran domain, (e.g., Gràcia et al, 2006;Gràcia et al, 2012;Martínez-García et al, 2013;Perea et al, 2018). The dominant tectonic feature of the Alboran is the complex fault network of a major left-lateral shear zone that extends for more than 400 km in roughly NE-SW from SE Spain across the Alboran Sea to the eastern Rif Mountains near Al Hoceima (Trans-Alboran Shear Zone, Bousquet, 1979;De Larouzière et al, 1988;Stich et al, 2006).…”

Tsunami Generation Potential of a Strike-slip Fault Tip in the Westernmost Mediterranean

“…1c and 2). Tectonic activity initiated along the Averroes Fault during the late early Pliocene 20,21,22,23 , giving it an age of 4.57 Ma 24,20 . Considering the age of the fault and the vertical offset along its northern segment, we calculate an average vertical slip rate of 0.1 mm/yr.…”